This invention relates to moisture control composition responsive to changes in humidity, particularly for use in odour absorbing and releasing media in a variety of applications for removing and masking odours and other volatiles caused by pets, house-hold rubbish, moulds, cigarettes, engine exhaust gases, cooking, human sweat and vegetable and animal decomposition.
Conventionally odour control in domestic situations has been by masking with air fresheners or by cleaning of soiled surfaces to remove the source of the odour. Absorption of malodourous liquids has also had some success.
Typical of this approach is the invention of U.S. Pat. No. 5,819,688 which discloses a mat of a cellulosic fibres bound with an acrylic latex and containing a zeolite mineral. The mat is claimed to be capable of being air dried and reused. A problem is that odours are released from the pad under drying conditions or if the pad is saturated.
U.S. Pat. No. 5,891,221 discloses an odour filtration device utilising hollow wicking fibres impregnated with a permanganate and carbonate or phosphate solution. This is placed in an air stream to remove gaseous odours. The solution flows through the fibres which are placed within a filter through which the air stream flows. This is a large scale system unsuitable for a wide variety of domestic and industrial odour problems.
U.S. Pat. No. 5,944,873 discloses a gas mask incorporating a noxious gas absorber utilising activated carbon, wherein the absorbed gas displaces an odorant as an alarm signal.
Another industrial scale system is disclosed in U.S. Pat. No. 5,236,878 discloses an odour absorbent consisting of a zeolite impregnated with a catalyst component. The adsorbed materials are desorbed by heating to regenerate the absorbent. It is an object of this invention to provide a liquid, volatiles and odour absorbing device that is effective and convenient to use.
To this end the present invention provides a package having at last one porous surface, and preferably being used for an absorbent device for liquid and gaseous contaminants, said package incorporating a particulate mixture formed by mixing together
a) 5 to 50% by weight of a water and/or water vapour absorbing agent
b) 10 to 60% of a water vapour absorbing and releasing agent
c) 5 to 50% of an absorbent for small molecules and/or
d) 5 to 60% by weight of an emulsion or solution of a mixture of odour masking and neutralising compounds impregnated in the particulate components and/or
e) up to 10% by weight of a water vapour activated active ingredient.
Surprisingly this device absorbs liquid and gaseous wastes in humid and dry atmosphere conditions and releases the odour masking and neutralising compounds. This effect may be due to synergistic interaction of the surfaces of the particulate blend in facilitating the absorption of water vapour and odour compounds and the release of water vapour and actives. This invention is partly predicated on the realization that water vapour has a significant influence on the release, carriage in air and perception, of gas or vapour phase molecules many of which are responsible for mal-odours. It appears that under higher relative humidity absorption of volatiles and malodorous compounds is improved and under lower relative humidity release of the odour masking compounds is enhanced. This invention finds application in any situation where humidity varies and absorption and/or release of gas or vapour phase molecules is required. The water vapour control provided by this invention is superior to that provided by silica gel and the quantity required is of the order of 10% of the weight of silica gel needed in similar applications. Thus the composition of this invention can be used in packaging electrical and electronic devices and in situations where humidity can affect the performance of machinery such as the paper feeding mechanisms in printers and photocopiers.
In particular this invention is applicable to control of odours which are generated by microbial activity and decomposition and are carried by vapours; including pet trays, nappies, room and cupboard deodorisers, coffins, caskets, cadaver bags and mausoleums, air conditioning systems, food storage and transport containers, industrial plants with volatile and gaseous materials, waste disposal containers and rubbish bins.
The present invention also lowers microbial activity of bacteria and fungi usually associated with absorbed wastes. This is apparently influenced by the reduction in available water and water vapour which in air is defined as relative humidity and this lowering of relative humidity in the air space around the device is an important condition for retarding bacterial and fungal growth. Bacterial and fungal activity is also inhibited by contact with the active compounds on the active surfaces of the absorbents and in the air space about them and on the open surfaces of putrescent materials. Thus the device of this invention is useful in slowing the growth of fungi particuarly moulds or bacteria. In tropical, humid locations moulds other fungi and even algae proliferate in closed systems like cupboards or boats. The device of this invention allows boats and cupboards to be closed and locked without encouraging wood rot, moulds and algal slimes. The water or water vapour absorbing agent is preferably a hygroscopic polymer capable of absorbing water or water vapour in large multiples of its mass which may be described as super absorbancy. A preferred class of super absorbent polymers are polyacrylate/polyalcohol copolymers such as that marketed by Cryovac which are capable of absorbing water up to 400 times their own mass. Optionally other hygroscopic substances such as calcium chloride may be included. Where the application is only to control odours in confined spaces the content of the polymer may be 5 to 20% by weight but where liquid waste is also to be dealt with the content is usually from 15 to 60% by weight.
The agent for absorbing and releasing water vapour is preferably a porous siliceous component which is preferably silicon dioxide, perlite [a dehydrated, exfoliated glassy siliceous material] and/or vermiculite [a hydrated silicate clay or montmorillonite]. These are selected on the basis of their high porosity, very large available surface area and high capillary lift. Capillary lift increases increasing surface area to volume ratio of the particles. This invention is partly predicated on the discovery that the siliceous material such as perlite interacts with the hygroscopic polymer to improve the sensitivity of the absorbent blend to changes in humidity. It appears to increase the affinity of the polymer for water and facilitates the mass flow of water vapour and volatiles into or out of the polymer.
The molecular absorbent consists of an oxygen scavenger and/or finely divided zeolite preferably clinoptilolilite, mordenite, attapulgite and/or activated carbon. The oxygen scavenger is used in situations where the oxygen present is to be removed permanently. A preferred oxygen scavenger is marketed by Cryovac in Australia under the tradename Everfresh. The Zeolite or activated carbon will absorb oxygen but is likely to release it again if the balance is not maintained. The molecular absorbent is preferably chosen for its ability to absorb nitrogen compounds such as ammonia, amines, cationic compounds and salts thereof. These compounds are the usual consequence of decomposition. However in particular applications such as controlling sulfur compounds, the molecular absorbent will be selected for its ability to absorb sulfur containing gases and vapours. Again high porosity, chemistry, binding efficacy, particle size and large available surface area are important characteristics.
For all the particulate components particle size and surface area affect performance. For the molecular absorbent in flow through applications increasing its particle size reduced the restriction of air flow through the sachet without affecting and reducing its capacity and affinity to absorb volatiles and odour molecules. For the porous siliceous component increasing the surface area increases the capillary lift and the rate at which the actives in the emulsion or solution are released.
The gas binding capability of the molecular absorbent is unexpectedly more effective under humid conditions and higher temperatures. It is thought that this may be because many of the odour molecules are associated with water vapour molecules and the silica and hygroscopic polymer in reducing the relative humidity around the device improves the absorption of the gases responsible for unwanted odours.
The mean particle size for each of the particulate components as well as the particle size distribution affect the performance of the pads. This may be adjusted by simple trialling for each application. In some applications the relative sizes of each of the 3 particulate components can also effect performance and again this can be determined by comparative trials.
The emulsion or solution contains as an active agent one or more of an algicidal, bacteriocidal, fungicidal, insecticidal, or odour masking or neutralising compounds. These may include a mixture of compounds selected from available terpene type compounds such as camphor, menthol, pine, eucalypt and ti-tree oils, terpenoids, compounds of essential oils including phenyl propanoids, aromatic alcohols, sulfur compounds and small molecular weight substituted isoprenes or other volatile compounds. The term terpene compounds as used in this specification includes odorants both synthetic and natural composed of terpenes [C10H16] sesqui terpenes, diterpenes and higher polymers and also oxygen containing compounds derived from terpene hydrocarbons such as alcohols, ketones and camphors.
The solution or emulsion of odour masking or neutralising compounds is preferably formed from pure water but may also be an oil or alcohol solution. Where an oil or other non aqueous solvent is used for the actives care must be taken to ensure that it does not inhibit the water vapour exchange function of the particulates. Oils such as safflower oil have been found to be suitable. Most odour masking or neutralising compounds are oil soluble rather than water soluble and may need to be emulsified with a suitable emulsifier that maintains the suspension of fine oil droplets in the aqueous phase of the emulsion. As some odour masking or neutralising compounds have some solubility in water a detergent may also be used to lower the surface tension of the aqueous constituents. This component may also include perfumes. The emulsion or solution includes from 0.01% by weight of active compounds and up to 60% by weight of emulsifiers, detergents or other surface active agents. The emulsion or solution may be formed from a concentrate comprising at least 0.5% of actives which is diluted by adding water to achieve dilution rates of 1/5 to 1/50. This diluted emulsion or solution is generally added at the rate of 10 to 70% by weight of the dry particulate components. It is preferred to add the emulsion or solution as the last component in forming the mixture which returns to a free flowing particulate mix or powder. The content of the active ingredient in the final particulate mixture is at least 0.006% by weight. The choice of the active ingredient has to take into account its susceptibility to be absorbed and released from the absorptive components. Care needs to be taken that the small molecule absorbing agents do not affect the release of the volatile actives. Because of the water absorption capability of the absorbents the odour masking or neutralising compounds are displaced into the vapour phase when the humidity is low effectively masking or neutralising any odours present. When humidity and/or temperature is higher the odours are absorbed together with the wafer vapour in the air around the device.
As well as odour masking or neutralising compounds the device of this invention can optionally include other active agents having biocidaql properties to control, insects, arthropods, arachnids, bacteria, fungi, algae or deodorising properties, or perfume properties or allergy lowering properties. These may include short chain aliphatic alcohols, low molecular weight organic acids including sorbic, citric and benzoic acids, urea, dimethyl sulfoxide, or metabisulfite for sulfur dioxide generation. Tea extracts, tannic acid compounds or thiocyanates may be used as lo an additional component where allergies from dust mites are a problem. Again allergenic activity is also related to humidity and the absorbent system of this invention acts as an effective delivery system. Inorganic salts or polyols may also be included to depress the freezing point of the emulsion where needed. Where the pads are used in conjunction with foodstuffs the actives are selected from approved food additives and adjuvants.
Where the actives are water vapour activated as in the case of metabisulfite it is not essential to add any aqueous phase.
Conveniently the device of the present invention is a package containing the absorbents in finely divided form. At least one portion of the surface of the package is porous to allow the easy transmission of gases, water and other vapours and liquids. Depending on the application the package may be a two sided bag or sachet or be contained in a rigid cassette or having one side impervious. Where the pad is to be applied in contact with a horizontal surface, it is preferable to have one side as an impermeable laminate sheet, to which double sided adhesive tape can be conveniently applied and which will not be limited in adhesion by the emulsified liquid.
Where the pads are intended to absorb large amounts of fluids or water, such pads will have a higher proportion of the hygroscopic polymer [polyacrylate/polyalcohol copolymer] and will be useful as for example absorbents in nappies, for incontinence and for pet litter trays etc.
In other applications both sides can be pervious to gases, volatiles and liquids. These are useful in air-flow impact applications such as air conditioning in vehicles or buildings. In air conditioning applications the molecular absorbent will be in higher concentrations. It has also been found that in flow through applications larger particle sizes for the particulate components is more appropriate to facilitate the passage of the air through the pads.
The preferred pervious material is a non woven fabric with a pore size capable of retaining the smallest absorbent particles after mixing. The material used for tea bags is suitable as the pervious material. Where an impervious backing sheet is required any material including laminates, capable of being easily adhered or heat sealed to the pervious sheet may be utilised. A food grade impervious laminate sheet has been used in the present invention and is suitable for lining the base of pet litter trays.
In forming the mixture it is usually convenient to mix the three particulate components and then add the solution or emulsion. The addition of the solution improves the handling of the mixture during mixing and packaging as it binds the finer particles and prevents their loss.
In use the pads are usually disposed porous face downwards at the top of the space to be treated. However when used in cassettes for air conditioning ducts or in electrical or battery generated heat activated odour releasing devices they may be inserted vertically. In air conditioning ducts, cassettes of filters of multiple pads should be placed obliquely across the air flow.
The pads singly or in sheets, mats or filters can be used in a wide range of applications including odour control in rooms, cupboards, dishwashers, refrigerators, air conditioning, rubbish bins, food transport containers, for moisture control in transport containers etc, electronic boards, photocopier paper trays for volatiles and moisture control in art conservation, applications involving compressed or pumped air and in the storage and of climacteric and other fruit and control of microbiological and biological organisms and/or gases and other volatiles for food transport and storage.
Various forms of the invention will be described in the following examples.
The polymer used in the following examples is Stockhausen AP85-38 a non hazardous white stable polyacrylate/polyalcohol copolymer. It is insoluble in water but is capable of absorbing up to 400 times its mass in water.
The Perlite used is available as Fernz P 200 an expanded white natural mineral stable from xe2x88x9225xc2x0 C. to 100xc2x0 C. The density is within the range 45-75 Kg/m3 It has a high surface area and high porosity and capillary lift of 13 mm/min @ 5 minutes and a water and oil absorption capacity of about 60% by volume.
The zeolite used in the following examples was obtained from Castle Mountain Zeolites in Quirindi. It is a fine pink powder and has a an SiO2: Al2O3 ratio of 5.7, a surface area of 28-39 m2/g and ammonia gas absorbency of up to 500 meq/100 g. Its functionality is to absorb gases such as methane, ammonia, hydrogen sulfide and ammoniacal compounds such as amines, urea derivatives and ammonium salts and cations such as sodium, calcium, magnesium, iron, zinc, copper.
The emulsion used in the following examples was formed by diluting a concentrate of an odour neutralizing complex marketed under the brand OCS-24 by Odour Control Solutions P/L of Narellan NSW Australia. The complex may be used in an oil carrier or as a water based emulsion. Surprisingly this complex is effective when used in the present invention in the reduction of the effect of volatile pollutants such as reduced thiols and mercaptans. The complex is composed of 22 essential oils of high purity and has the following approximate composition by volume:
Manufacturing Technique
The dry ingredients are mixed to ensure an even distribution of particle sizes and then blended with the emulsion so that the ingredients were still free flowing and not aggregating. In forming the mixture it is usually convenient to mix the three particulate components and then add the solution or emulsion. The addition of the solution improves the handling of the mixture during mixing and packaging as it binds the finer particles and prevents their loss. Care is required to ensure that the bulk density of the perlite is consistent when batching. The admixture of the emulsion is controlled by its interaction with the perlite.
When the liquid is added to the to the combined dry ingredients
1. the mixing vessel and any storage container used prior to, during and subsequent to manufacture must be covered with a well fitting air-tight lid to prevent loss of volatiles;
2. manufacturing must occur in an air conditioned room that is both dehumidified and cooled to reduce the possibility of moisture ingress into the mixture, given its propensity andcapacity to sequester moisture from air and release of volatiles;
3. bulk pads when manufactured must be stored flat and not too high one on top of the other, so that only minimal, light pressure is applied to prevent squeezing out of the liquid;
4. Ensure that there is no stratification of particle sizes before the pads are filled.
Pad Behaviour
The mass of the pads made according to the formulations of this invention will vary over time due to changes in humidity. Absolute Humidity determines pad mass with a linear increase in weight with increasing humidity.
Increasing temperature at a low relative humidity [RH] [xcx9c20%] increased mass at first and then decreased mass. This seems to be the sum of three effects namely time rate of change of mass, Absolute humidity [mass of water in the air] and dehydration due to rising temperature.
Increasing temperature at constant high RH [xcx9c90%] increased equilibrium mass in an exponential manner.
Increasing RH at constant temperature gave a modest increase in pad mass. At higher temperatures this effect was more marked but below 20xc2x0 C. there was little effect. Above 30xc2x0 C. and high RH a 5xc2x0 C. increase in temperature would add about 1 gram in weight to a pad whose initial weight was 2.4 grams.
The speed of moisture uptake increased with increasing amounts of the capillary lift agent [preferably perlite]. Speed of uptake measured as time rate of change of pad mass increased with increasing surface area for the same mass of capillary lift agent.
Increasing the proportion of the super absorbent polymer increased the magnitude of mass change in the pad.
The mass of the pads will cycle over a 24 hour period and 2.4 gram pads have exhibited mass varying from 1.7 grams to 3.5 grams in waste bins and from 1.9 to 10 grams in dishwashers. Generally the pads will lose mass during the day with higher temperatures and lower RH and gain mass at night with lower temperatures and higher RH and dew point is generally an indication of the largest mass.
At constant conditions such as air conditioned rooms at a constant 18xc2x0 C. and 50% RH a 2.4 gram pad in a bin was 1.8 grams while in a hot house at 37xc2x0 C. and  greater than 80% RH the mass stabilised at 3.5 grams.
Under tropical conditions the minimum mass of the pads gradually increased over several days. The cycling amplitude becomes slightly damped over time. The daily cycling behaviour of the pads is very variable depending on the temperature and RH in the immediate vicinity of the pad.
The effective control of malodours is affected by the binding capacity of the molecular adsorbent [preferably zeolite]. When all the binding sites are filled the pad releases odours back into the environment. Odour control is improved by the inclusion of a (micro)biocide in the active ingredients along with odour masking compounds. It is believed that when the pads are absorbing moisture they are also binding associated vapour phase odour molecules and when they are releasing moisture they are preferentially releasing vapour phase actives such as (micro)biocides or odour masking compounds.
The pads of this invention are particularly suitable for battery powered or cassettes for use in electrically heated odour control devices. Pads of this invention when subjected to resistance heating in such devices quickly lose mass and when the devices are switched off they regain mass.